User Tools

Site Tools


hibernate_from_a_non_activate_swapfile_from_btrfs

Hibernate from a non activate swapfile from btrfs

* Important! * This didn't work! It is not secure! When wiping happens, the file gets moved to another place by btrfs, then, this doesn't work for two reasons: 1) Wiping happens in other parts of the disk, and the offset changes and has to be updated in all configurations files after wiping everytime.

* This was just a stupid experiment.

Create swapfile

  • Create a separate swap volume (not necessary)
sudo btrfs subvolume create /mnt/btrfsbase/swap

* Add it to /etc/fstab
UUID=8f9ede3a-912f-40d6-9335-90ed3186e3e4   		      	    /swap	      	     btrfs defaults,noautodefrag,nodatacow,nodiscard,noatime,subvol=swap	0 0
  • Be sure there is no discard nor autodefrag options activated for this subvolume
  • Create a swapfile
cd /swap
sudo truncate -s 0 swapfile
sudo chattr +C swapfile
btrfs property set swapfile compression none
sudo chmod 600 swapfile
sudo dd if=/dev/zero of=swapfile bs=1M count=24576 #reserve 24GB
sudo mkswap /swap/swapfile

Find out resume device and offset

  • Find out resume device:
sudo findmnt -no UUID -T /swap/swapfile
gcc -O2 -o btrfs_map_physical btrfs_map_physical.c
  • Calculate offset
  • Write down the last number from the output of the following command:
sudo btrfs_map_physical /swap/swapfile | head -n 2
  • Result:
FILE OFFSET	FILE SIZE	EXTENT OFFSET	EXTENT TYPE	LOGICAL SIZE	LOGICAL OFFSET	PHYSICAL SIZE	DEVID	PHYSICAL OFFSET
0	134217728	0	regular	134217728	4594864128	134217728	1	4594864128
  • Write down the output of the following command:
sudo getconf PAGESIZE
Result: 4096
  • Calculate offset: Divide the first number under the PAGESIZE: offset = PHYSICAL_OFFSET/PAGESIZE

4594864128/4096=1121793

Configure system for hibernation

  • Create /etc/initramfs-tools/conf.d/resume and put the resume and offset data on it:
RESUME=UUID=8f9ede3a-912f-40d6-9335-90ed3186e3e4 resume_offset=1121793
  • Modify /etc/default/grub with the corresponding resume and offset values:
GRUB_CMDLINE_LINUX_DEFAULT="resume=UUID=8f9ede3a-912f-40d6-9335-90ed3186e3e4 resume_offset=1121793 quiet btusb.enable_autosuspend=n"
  • Activate the swap file
sudo swapon /swap/swapfile
  • Install uswsusp package
  • Edit /etc/uswsusp.conf:
resume device = /dev/disk/by-uuid/8f9ede3a-912f-40d6-9335-90ed3186e3e4
early writeout = y
image size = 0
RSA key file = /etc/uswsusp.key
shutdown method = platform
resume offset = 1121793
  • Activate a systemd service:
sudo systemctl edit systemd-hibernate.service
  • With:
[Service]
ExecStart=
ExecStartPre=-/bin/run-parts -v -a pre /lib/systemd/system-sleep
ExecStart=/usr/sbin/s2disk
ExecStartPost=-/bin/run-parts -v --reverse -a post /lib/systemd/system-sleep
  • Update initramfs and grub
sudo update-grub
sudo update-initramfs -k all -u
sudo update-grub
  • Test the hibernation:
sudo s2disk

I have a system with encrypted swap, but I don't want to have encryption on the hibernation swap file. My idea is to use hibernation only when strictly necessary, because I don't want to need to put a password during booting. Then, this swap file should actually be always deactivated except before hibernation. When resuming, this swap space should be deactivated and then securely wiped! The script to do this would be this: my_server_hibernate.sh:

#!/bin/bash

echo "Activating swap from swapfile"
sudo swapon /swap/swapfile
sleep 1
echo "Hibernating"
sleep 0.2
xtrlock -b &
sudo s2disk
echo "Returning from Hibernate"
sleep 10
echo "Deactivating swapfile"
sudo swapoff /swap/swapfile
sleep 5
echo "Wiping swapfile"
#sudo wipe -k -f -q -Q 1 /swap/swapfile
sudo dd if=/dev/zero of=/swap/swapfile bs=1M count=24576 status=progress #reserve 24GB
sync
sleep 1
echo "Making swapfs again"
sudo mkswap /swap/swapfile
echo "All done, ready to hiberante again"

References

hibernate_from_a_non_activate_swapfile_from_btrfs.txt · Last modified: 2021/01/31 23:55 (external edit)